Parts of the source code which underpins multi-billionaire Elon Musk's social media platform have been leaked online, Twitter says.

It says the code was posted on GitHub, a Microsoft-owned service where software developers share code.

It has now been taken down after Twitter requested its removal.

Separately, Mr Musk has reportedly signalled to Twitter workers that the firm is worth less than half the $44bn (£36bn) he paid for it last year.

"GitHub does not generally comment on decisions to remove content. However, in the interest of transparency, we share every DMCA [Digital Millennium Copyright Act] takedown request publicly," a GitHub spokesperson told the BBC.

The DMCA was signed into law in the US in 1998. It is aimed at protecting copyrighted material on the internet.

In the takedown request, Twitter called on GitHub to provide information on who was behind the account which leaked the code-named FreeSpeechEnthusiast.

San Francisco-based Twitter said in the filing that the account had infringed copyrights owned by the company.

The leak creates a new challenge for Mr Musk, who has slashed Twitter's workforce by more than a third and faced an exodus of advertisers since buying the platform in October last year.

Meanwhile, the Tesla chief executive has reportedly indicated that Twitter is now valued at less than $20bn.

The estimate of the company's value was based on Mr Musk's offer of stock grants to staff, according to technology news websites Platformer and the Information, which first reported the story.

Mr Musk also reportedly told staff: "I see a clear, but difficult, path to a >$250B valuation," which suggests a more than tenfold increase in Twitter's valuation.

In response to a BBC request for comment Twitter's press office email account automatically responded with a poo emoji, an approach that Mr Musk announced in a tweet earlier this month.